The present invention is generally directed to ink jet compositions useful in various imaging systems; and more specifically, the present invention is directed to sulfonated trisazo black dyes useful in ink jet printing processes. Accordingly, in one embodiment of the present invention there is provided aqueous ink compositions having incorporated therein nonmutagenic sulfonated trisazo black dyes. Moreover, the ink jet compositions of the present invention have improved waterfastness in comparison to several of the prior art compositions; and furthermore, the substantivity of the sulfonated trisazo dyes illustrated hereinafter in addition to possessing the desirable property of nonmutagenicity have improved affinity for various substrates such as paper.
Compositions useful in ink jet printing systems are well known, which compositions generally contain water soluble dyes. There is thus disclosed, for example in U.S. Pat. No. 3,846,141, an ink composition useful in jet printing, comprised of an aqueous solution of a water-soluble dye and a humectant material formed of a mixture of a lower alkoxy triglycol, and at least one other compound selected from the group consisting of a polyethylene glycol, a lower alkyl ether of diethylene glycol, and glycerol. According to the disclosure of this patent, such printing inks have the desired viscosity for use in jet printing in that the viscosity of the composition is subjected to little variation with use as water is lost by evaporation during recirculation of the ink composition through the jet printer. Moreover, apparently the humectant system disclosed in this patent substantially prevents or minimizes tip drying of the printing ink in the orifice or nozzle during down time of the printer, such as when the printer is rendered inoperative. As further disclosed in this patent, the basic imaging technique in jet printing involves the use of one or more ink jet assemblies connected to a pressurized source of ink. Each individual ink jet includes a very small orifice usually of a diameter of 0.0024 inches, which is energized by magneto restrictive piezo-electric means for the purpose of emitting a continuous stream of uniform droplets of ink at a rate of 33 to 75 kilohertz. This stream of droplets is desirably directed onto the surface of a moving web of, for example, paper; and is controlled to form printed characters in response to video signals derived from an electronic character generator and in response to an electrostatic deflection system.
Also, there is disclosed in U.S. Pat. No. 4,279,653 ink jet compositions containing water-soluble wetting agents, a water-soluble dye and an oxygen absorber. Similarly, U.S. Pat. No. 4,196,007 describes an ink jet printing composition containing an aqueous solution of a water-soluble dye and a humectant consisting of at least one water-soluble unsaturated compound. Other patents disclosing aqueous inks for ink jet printing include U.S. Pat. Nos. 4,101,329; 4,290,072 and 4,299,630.
Furthermore, disclosed in U.S. Pat. No. 4,383,859 are processes for the preparation of inks wherein the ink concentrate is processed in a specific manner including subjecting it to the operational stress of an elevated temperature of about 50.degree. C. Examples of useful dyes selected for the aforementioned process include purified nigrosine dyes, reference column 3, beginning at line 58. According to the disclosure of this patent, the invention offers a specific advantage of nigrosine dye in an ink in that high concentrations of this dye can be selected, and further it is toxicologically a safe dye, reference column 4, beginning at line 18.
There is disclosed in U.S. Pat. No. 4,235,773 trisazo dyestuffs which are suitable for dyeing natural or synthetic fiber materials, such as cotton, regenerated cellulose, wool and paper. A similar teaching is present in U.S. Pat. No. 4,255,327 which discloses a new group of trisazo compounds that are useful as direct dyes for cellulose textiles, paper, and leather. These dyes, which were intended to replace the widely used paper dye known as C.I. Direct Black 38, are water-soluble tri or tetrasulfonic acid compounds of the structure as illustrated in column 1, beginning at line 1, for example. Also, a similar teaching is provided in U.S. Pat. Nos. 4,270,814; 4,443,371 and 4,286,989. While the present invention is directed to ink jet compositions having incorporated therein similar dyes as disclosed in these prior patents, which are mutagenic to various extents in that they fail the Ames tests, an important critical difference resides in the use of specific sulfonated dyes which are nonmutagenic as indicated hereinafter.
Accordingly, thus there continues to be a need for new inks for ink jet printing and processes for preparing these compositions. Additionally, there continues to be a need for ink jet compositions, which when in use result in superior optical print densities, and have excellent waterfastness characteristics. Moreover, there is a need for new dyes possessing desirable nonmutagenic characteristics enabling them to be safely used in ink jet printing processes.